1. Field of the Invention
The present invention relates to a transflective liquid crystal display device implementing a color filter having various thicknesses, and more particularly, to a method of forming a color filter having various thicknesses.
2. Description of the Related Art
Liquid crystal display (LCD) devices are widely used as displays in devices such as portable televisions and notebook computers. Liquid crystal display devices are classified into two types. One is a transmissive type liquid crystal display device using a backlight as a light source, and another is the reflective type liquid crystal display device using an external (or ambient) light source, such as sunlight or a lamp. It is difficult to decrease the weight, volume, and power consumption of the transmissive type LCD due to the power requirements of the backlight component. The reflective type LCD has the advantage of not requiring a backlight component, but cannot operate without an external light source.
In order to overcome the drawbacks of these two types of LCDs, a transflective LCD device which can operate as both a reflective and transmissive type LCD is disclosed. The transflective LCD device has a reflective electrode in a pixel region, wherein the reflective electrode has a transmissive portion. Thus, the transflective LCD device has lower power consumption than the conventional transmissive type LCD device because a backlight component is not used when there is a bright external light. Further, in comparison with the reflective type LCD device, the transflective LCD device has the advantage of operating as a transmissive type LCD device using backlight when no external light is available.
FIG. 1, a sectional view of a conventional transflective LCD device, helps to illustrate the operation of such devices. As shown in FIG. 1, the conventional transflective LCD device includes a lower substrate 100 (also referred to as an array substrate), an upper substrate 160 and a liquid crystal layer 130 interposed therebetween. A common electrode 140 and a color filter 150 are formed on the upper substrate 160. An insulating layer 110 and a reflective electrode 120 are formed on the lower substrate 100, wherein the reflective electrode 120 has an opaque portion 122 and a transparent portion 124. The opaque portion 122 of the reflective electrode 120 can be an aluminum layer and the transparent portion 124 of the reflective electrode 120 can be an ITO (indium tin oxide) layer. The opaque portion 122 reflects the ambient light 170, while the transparent portion 124 transmits light 180 from the backlight device (not shown). The liquid crystal layer 130 includes a plurality of spherical spacers (not shown) used to keep a fixed layer thickness or cell gap of the liquid crystal layer 130. Thus, the transflective LCD device is operable in both a reflective mode and a transmissive mode.
The conventional transflective LCD device, however, has the drawback of different color reproduction levels (color purity) in reflective and transmissive modes, due to, referring to FIG. 1, the backlight 180 penetrating the transparent portion 124 passing through the color filter 150 once and the ambient light 170 reflected from the opaque portion 122 passing through the color filter 150 twice. This greatly degrades the display quality of transflective LCDs.
Recently, a method of forming a color filter having various thicknesses on a substrate, to resolve the color purity issue, has been disclosed. FIGS. 2A˜2C are sequential sectional views illustrating a fabricating process for the color filter having various thicknesses according to the prior art.
In FIG. 2A, a transparent resist layer 210 is coated and patterned on a substrate 200 (e.g. the upper substrate). The transparent resist layer 210 corresponds to a reflective region 201 of a transflective LCD device.
In FIG. 2B, a patterned red resist layer 220 is coated and patterned on part of the substrate 200 and part of the transparent resist layer 210.
In FIG. 2C, a patterned green resist layer 230 and a patterned blue resist layer 240 are sequentially coated and patterned on part of the substrate 200 and part of the transparent resist layer 210. Thus, a conventional color filter having various thicknesses is obtained.
Nevertheless, the method requires additional photolithography (that is, an added mask) to form the transparent resist layer 210, and thereby increases costs. Referring to FIG. 2C, since the resist layers 220, 230 and 240 are coated on the rough substrate surface having the transparent resist layer 210; it is difficult to control the thicknesses of the resist layers 220, 230 and 240. The conventional method, however, cannot exactly solve the problem of different levels of color purity.